Thousands of Russians have marched in the capital, Moscow, in memory of Boris Nemtsov, an opposition leader murdered two years ago, calling for further investigations into his killing.

Nemtsov, a former deputy prime minister who became an outspoken critic of longtime President Vladimir Putin, was shot in February 2015 while walking across a bridge a short distance from the Kremlin with his Ukrainian girlfriend.

At the time, Nemtsov, 55, was working on a report that he said proved Russia's direct involvement in a separatist rebellion that has raged in eastern Ukraine since April 2014. Russia has denied the accusations.

Five men accused of murdering Nemtsov went on trial in October 2016.

Some marchers on Sunday in Moscow carried Nemtsov's portraits, Russian flags and placards with slogans such as "Russia without Putin".

"We gathered here to demand bringing of Boris Nemtsov's killers to justice, not only its performers but also its organisers and those who ordered it," Ilya Yashin, a Russian opposition activist and an organiser of the march, told Reuters news agency.

"We gathered here to demand political reforms and release of political prisoners."

Police put the number of marchers at 5,000, but a group of voluntary observers said there were more than 15,000 demonstrators.

more March to remember murdered Kremlin critic Boris Nemtsov | Russia News | Al Jazeera